Using a low-energy Ar+ ion-beam with and without a reactive gas, chemically stable poly(tetrafluoroethylene) (PTFE) films were modified to have special surface features. The adhesion strength between the PTFE and the copper was significantly improved because of both changes in the surface topography and chemical interactions due to PTFE functionalization (oxidation and amination). The surface modification altered the failure mode from adhesive failure for the unmodified PTFE/Cu interface to cohesive failure for the surface-modified PTFE/Cu layer interface.